Ink jet printing has replaced or complemented in many fields the classical methods of image reproduction. Although ink jet printing has reached a remarkable degree of maturity, further improvements are still necessary, in particular in the graphic and the photographic field. Modern ink jet printers need to furnish in these fields optimal prints on a wide variety of recording sheets such as polymer-based recording sheets or rapidly drying nanoporous recording sheets. In these fields, stability against light and oxidative gases (ozone, NOX), but also a big volume of color space (gamut) of the printed images is primordial. This can be achieved only by using a finely tuned system of recording liquids (respectively the dyes contained therein) adapted to these recording sheets.
Most of the commercially available magenta dyes that are used in recording liquids for ink jet printing do not satisfy all the necessary requirements in combinations with polymer-based and nanoporous recording sheets. The magenta dyes used nowadays do not have all required properties, such as a suitable hue, a very high brilliance (saturation), good light stability, good resistance against degradation by ozone, no dye aggregation on the surface of the recording sheet (“bronzing”), excellent diffusion fastness and excellent solubility and low viscosity in the mainly aqueous recording liquids.
Although quite a number of different magenta dyes have already been proposed as dyes for ink jet printing, none meets all the necessary requirements.
The magenta dyes of formula (I) (example no. 25)
and of formula (II) (example no. 27)
are described in patent application WO 98/11,167.
These anthrapyridone dyes, representing the state of the art, do not satisfy all the required demands if they are used in the formulation of recording liquids for ink jet printing that should provide magenta images or colorings having a pure and as far as possible bluish hue (values of L*a*b* with elevated values of b*) on any type of recording sheet such as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials. They also should not induce a viscosity increase in the aqueous recording liquids.
Dyes used in such recording liquids need to have a high solubility in the essentially aqueous recording liquid, they have to penetrate into the recording sheet and should not show dye aggregation on the surface of the recording sheet (“bronzing”). They need to provide printed images having high optical density, good water fastness, good light stability and good storage stability even under adverse conditions. They need to be stable in the recording liquid even when the recording liquid is stored for a long time under adverse conditions. Various types of compositions have been proposed as recording liquids. Typical recording liquids comprise one or more dyes or pigments, water, organic co-solvents and other ingredients.
The recording liquids have to satisfy the following criteria:                (1) The recording liquid gives images of excellent quality on any type of recording sheet.        (2) The recording liquid gives images exhibiting good water fastness.        (3) The recording liquid gives images exhibiting good light stability.        (4) The recording liquid gives images exhibiting excellent abrasion resistance.        (5) The recording liquid gives images exhibiting excellent storage stability under conditions of high temperature and humidity.        (6) The recording liquid does not clog jetting nozzles of the ink jet printers even when these are kept uncapped while recording is suspended for long periods.        (7) The recording liquid may be stored for long periods without deterioration of its quality.        (8) The physical properties of the recording liquids, such as viscosity, conductivity and surface tension are all within defined ranges well suited for the intended use.        (9) The recording liquid has to be non-toxic, non-flammable and safe.        